Solar cells are electrical devices that convert light energy directly to electricity by the photovoltaic effect. The cells are gaining increasing popularity as energy source as their efficiency improves and the world looks for energy sources that do not generate greenhouse gasses. Some solar cells include a copper indium gallium selenide (“CIGS”) semiconductor material that is used in thin-film solar cells. While sodium doping has been found to improve the performance of CIGS solar cells, there is currently limited control of the Na dosing.